The onset of puberty in the female involves a complex series of integrated neuroendocrine morphological events. The brain-pituitary-gonadal-adrenal axis matures as a result of precise, yet sometimes subtle, changes in serum hormone concentrations simultaneous with the development of negative and positive feedback mechanisms associated with releasing factors and pituitary tropic hormone release or inhibition. Just prior to puberty all of the events are synchronized and lead to vaginal opening and first ovulation. A primary focus of this study is an examination of the changing sensitivity of the hypothalamic-pituitary complex to estrogen feedback just prior to puberty. Pituitary release of LH in response to LH-RH treatment, bilateral anterior hypothalamic lesions placed on day 15, or chronic estrogen maintenance of ovariectomized females by estradiol polyethylene capsule implants will be examined between days 30 and 36. Multiple blood samples will also be drawn from an atrial cannula over a ninety-minute period to examine the pulsatile release of LH following ovariectomy on day 25 in the prepubertal animal and how this secretory pattern is influenced by estrogen treatment or anterior hypothalamic lesions. Finally, using immunocytochemical techniques, we will examine the LH-RH neuronal system in the normal, prepubertal female rat between days 20 and 36, and how the presence of immunoreactive LH-RH may be influenced by brain lesioning, estrogen treatment, or ovariectomy.